Extruded pipe made from lead alloys



Patented Oct. 15, 1946 EXTRUDED PIPE MADE FROM LEAD ALLOYS William Thomas Butcher and Arnold Lloyd, Greenford, England, assignors to Goodlass Wall & Lead Industries Limited, Oxted, England No Drawing. Application January 23, 1945, Serial No. 574,218. In Great Britain January 4,

1 Claim.

From our investigations on lead pipes we find that two of the most important characteristics necessary for satisfactory service are, first a high degree of resistance to steady internal pressures such as are met with in water distribution, and second a tensile strength adequate to resist pressure surges of higher intensity which occur in practically all piping systems.

In order to meet the above conditions various alloys of lead have been suggested, but it has under internal pressure, and an increased tensile strength as compared with lead pipes at present in use.

The lead alloy pipes h therto suggested usually have a fine-grained crystal structure. This structure in a lead pipe ensures a uniform distribution of stresses in the pipe walls which prevents localised expansions under service conditions.

An important characteristic of lead alloy pipes as hitherto proposed is that for a given composition, refinement of grain size is accompanied by a reduction in resistance to steady pressures. This is well known and in order to employ these alloys in the manufacture of pipes having a satisfactory resistance to prolonged internal pressures, steps must be taken during extrusion to prevent the production of too fine a grain size.

It has been found that pipes made according to the invention, which have a fine grain size, have a much greater resistanc to prolonged internal pressure than similar pipes made with lead or other lead alloys.

The invention consists in a tube or other extruded section made of an alloy of lead and silver containing a relatively high proportion of silver of the order of 1.0%. We do not, howev r, exclude the possibility of the alloy containing other ingradients in quantities small in relation to the quantity of silver.

Lead tubes made from such silver lead alloys have a high resistance to prolonged internal pressure, and a high creep strength which is a measure of the capacity to resist expansion from internal pressure. These properties of silver lead alloys compared with lead are shown in the tables below.

1. Prolonged internal pressure tests Material Size Pressure Result Lead pipe x 3 lbs. per 340 lbs. per Burst after 7 yard. sq. 111. days life. 0.8% silver lead 34 x 3 lbs. per 340 lbs. per Unbroken at alloy pipe. yard. sq. in. 300 days.

1.0% silver lead x 3 lbs. per 340 lbs. per Unbroken at alloy pipe. yard. sq. m. 350 days.

2. Creep tests [Load 500 lbs. per square inch] Percent extension 1n- Material 100 days 200 days 400 days Lead pipe 3.57 5.77" 9.57. 0.%% silver lead al- Less than 0.1%.. 0.1%.... 0.2% (300 days).

my pipe. 1.0% silver lead 211- 0.1% 0.15%... 0.3%.

lov pipe. 1.26% silverlead 211- 0.15% 0.2%.... 0.2%.

10y pipe.

[Load 650 lbs. per square inch] Percent extension in- Material 100 days 200 days 300 days 500 days Lead pipe-- 18% Failed 190 d a y s 42%. 0.8% silver lead 0.34%"... 0.8% 1.2%...... Not deteralloy pipe. mlned. 1.0% silver lead 0.43%..-" 0.6% 0.7% 1.4%.

alloy pipe. 1.26% silver lead Less than Not deter- Not deter- Not deteralloy pipe. 0.1%. mined. mined. mined.

[Load 800 lbs. per square inch] Percent extension in- 45 Material 100 days 200 days 300 days Lead pipe Life 40 days 0.5% silver lead 211- 11% 25%..." Life 318 days,

10 p pe. 82%. 071% s lver lead 211 1.4% 3.5%.... 5.4%. loy pipe.

0.8% silver lead 211- 1.0% 2.0% 3.0%.

loy pipe. 1.0% silver lead al- 1.10% 1.42% 3%.

loy pipe. 1.26% s lver lead al- Less than 1.0%,

loy pipe. 300 days.

[Load 1000 lbs. per square inch] Per cent extension in- Material 60 days 100 days 200 days 300 days Lead pipe Failed in 21 days 0.5% silver lead 50% Failed 110 alloy pipe. (1 a y s 78%. 0.71% silver lead 2% 4.7% 12% 25%.

alloy pipe. 0.8% silver lead 1.5% 3.2% 9% 19%.

alloypipe. 1.0% silver lead 0.8% l. 1.6% 3.8% 8.8%.

alloy pipe. 1.26% silver lead 0.6% 0.81%. 2.0% 2.9%.

alloy pipe. 1.51% silver lead 0.2% Not dtter- Not detcr- N ot deteralloy pipe. mined mined. mined.

From these results it is apparent that tubes made from silver alloy of lead containing'from 0.7% silver to 1.5% silver have an exceptionally high resistance to creep under all loads from 500 to 1000 lbs. per square inch. Our researches have shown that the high resistance to creep which is characteristic of the extruded products according to the invention first appears-when the silver content of the lead alloy reaches the lower limit of 0.7% and the above table make clear that the creep resistance of tubes made of a lead alloy containing only 0.5% silver is of a different and much lower order, being comparable with that of the tubes made of refined lead containing .005 .0l% silver which we' have described in British Patent No. 538,295. We have not experimented with alloys containing more than 1.51% silver, but we do not believe that the upper limit of 1.5% silver recited in the appended claim is critical in the sense that the improved creep resistance disappears in the case of alloys containing a somewhat higher proportion of silver. The high cost of silver however imposes an economic upper limit beyond which it is unprofitable to go. We believe that, for practical purposes, the most satisfactory alloy for the manufacture of extruded sections according to the invention is one containing about 1% silver.

Along with the increased resistance to steady internal pressures we have found that the tensile strength of tubes made according to the invention is substantially increased as compared with that of lead which is 2200 lbs. per square inch. This will be apparent from the following table, which indicates the experimental results we have obtained:

Tensile strength,

- lbs. per sq. in. 0.71% silver lead 3200 0.8% silver lead; 3510 1.0% silver lead 3360 1.26% silver lead 3480 1.5% silver lead 3820 In our experience the extrusion temperature of the lead alloy is not critical from the point of View of creep resistance of extruded pipe and a wide range of extrusion press temperatures can be employed without adverse effect on the creep strength of the allow pipe.

. It will be appreciated that pipes made according to the invention in View of their higher ten. sile strength and creep resistance, can be made with thinner walls and therefore of less weight than the lead pipe at present in use for water supply purposes, and yet be equally as efiective.

While the primary application of the invention is to pipes it may also be applied to sheathings for cables or other tubular bodies which are exposed to prolonged internal pressure from fluids, e. g. fluids employed for the purpose of improving the insulation of a cable, or to other extruded products, e. g. extruded strip, which may be subjected to continuous steady loads Reference to "pipes herein is therefore intended to cover not only the usual conduit for fluid under pressure, but cable sheating and the like which is subjected to stresses byfiuid pressure. I

What we claim as our invention and desire to secu're'by Letters Patent is: i

' An extruded pipe for use under conditions requiring high creep resistance and high tensile strength, said pipe being composed of lead and silver containing from 0.7% to 1.5% of silver, the balance being substantially lead.

WILLIAM THOMAS BUTCHER. ARNOLD LLOYD. 

